There is a famous argument between Ramban and Maimonides
on the purpose of sacrifice. Maimonides writes in his great work
the Guide for the Perplexed (Book III, Chap. 46) that the purpose
of sacrifice is to eradicate false notions that certain species
of animals were deities. By sacrificing to G-d, the heathens'
worshiped species, we counter the problem, as Maimonides writes:

"....In order to eradicate these false principles,
the law commands us to offer sacrifices only of these three kinds:
'Ye shall bring your offering of cattle, of the herd and of the
flock' (Lev. 1:2). Thus the very act which considered by the
heathen as the greatest crime, is the means of approaching G-d,
and obtaining His pardon for our sins. In this manner, evil principles,
the diseases of the human soul, are cured by other principles
which are diametrically opposite."

Ramban argues vehemently on Maimonides in the beginning of
his commentary in the book of Leviticus (Lev. 1:9). There, Ramban
lodges two salient arguments:

1) We see that sacrifice existed in the days of Adam's son
Able, and in Noah's days when idolatry of this kind did not yet
exist. Therefore Maimonides cannot be correct to suggest that
sacrifice is to function to remove idolatrous notions.

2) Sacrifice is really viewed as an approach to G-d, as shown
by Bilaam's offerings, not a neutralizing procedure. How can
sacrifice be a negative, i.e., an agent countering idolatry,
when it is described as a positive, "a pleasant fragrance".

These questions certainly require a response. But I wondered,
is Ramban really suggesting that Maimonides was ignorant of the
stories in every Torah, that of Able, and Noach and Bilaam? This
possibility is absurd. So what exactly is Ramban saying when
quoting the facts that these early individuals offered sacrifice?

We are forced to say that Maimonides knew very well that
sacrifice existed prior to the command at Sinai. Perhaps then,
Maimonides' reasoning is that the Sinaic command
of sacrifice is that alone to which he refers which is to counter
idolatry. But cases prior to the Sinaic command of sacrifice
were not for the eradication of idolatry. But again, this answer
is far too basic that someone like a Ramban would not consider.
I am of the opinion that Ramban considered this answer, and yet,
still lodged his arguments against Maimonides.

Perhaps Ramban held that even with the sacrificial command
at Sinai, sacrifice can not be removed from its original form.
This I believe to be the pivotal point between Ramban and Maimonides.

Ramban held that although a new command and Torah system
was given, nonetheless, if sacrifice had an inceptional structure,
i.e., to approach G-d, it cannot deviate from this form. It may
have incorporated additional purposes at Sinai, but it cannot
be exclusively to eradicate idolatry as Maimonides holds. There
is sound reasoning as to why Ramban takes this approach. When
something comes into existence, its form at that moment is integral
to its definition. Water was created in a moist state, and as
such, it is inherently moist. Water without moisture is not water.
Once dust was created inherently dry, this feature forms part
of its very definition. So also, sacrifice at Adam's, Able's
and Noah's time, emerged as man's own attempt to approach G-d.
Since this is the very inception of the institution of sacrifice,
sacrifice by nature is an approach to G-d, and cannot be viewed
as lacking this property. Sacrifice without approach to G-d is
no longer sacrifice, according to Ramban. Based on this reasoning,
Ramban held that sacrifice could not be defined solely as that
which eradicates idolatry. It must - by definition - include
the inceptional property of an approach to G-d.

However, Maimonides was of the opinion that although sacrifice
came into existence in this form, as Ramban says, nonetheless,
Sinai has the ability to redefine its structure from the ground
up, and completely undermine its original nature. But this addresses
Ramban's second argument alone, dealing with the structure
of sacrifice. I believe his first argument to be dealing with
the goal of sacrifice. There, Ramban is of the opinion
that just as the structure cannot deviate, so also the goal of
approaching G-d must be an inherent property of sacrifice. It
is for this reason that Ramban gives two arguments, as each addresses
an additional point of contention Ramban had with Maimonides'
view.

According to Maimonides, Sinai had the ability to take an
institution and completely redefine it. The new reality of "national
commandments" given at Sinai are so overwhelmingly objective
in their truth, so real, as they emanate from G-d as part of
His Will, that commandments go so far as to define what truth
is. The Sinaic Commandments redefined reality for the
Jew. Sacrifice according to Maimonides for all halachik
intents and purposes didn't exist prior to Sinai. Historically
it did, but now as the Jews had new laws governing their lives,
previously known activities were only similar in name, and nothing
else. Sacrifice prior and subsequent to Sinai were as divergent
in nature as are color and weight. This was clear to Maimonides,
and he therefore had no qualms about explaining sacrifice as
if it never existed before.

Ramban was of the opinion that although Sinai redefines our
actions, it only adds the nature of 'command' to a preexisting
institution of sacrifice, but it does not redefine its original
nature.